Personal respiratory protection devices, also known as respirators or face masks are used in a wide variety of applications where it is desired to protect the human respiratory system from air borne particulates or noxious or unpleasant gases. Generally such respirators are in either a moulded cup-shape, such as those discussed in U.S. Pat. No. 4,827,924, or flat-folded format, such as those discussed in EP 814 871.
Moulded cup-shaped masks typically comprise at least one layer of a filter media supported by either an inner and/or an outer support shell. A gasket is provided around the inner edge of the cup-shape to ensure a good fit against the face of the wearer. The gasket is usually formed from a flexible material such that it moulds around the facial features of the wearer, providing a seal and good engagement between the mask and the face of the wearer. The quality of the fit of such respirators should be high, since it is essential that as much air as possible passes through the filter media and not around the edges of the respirator in use. Such respirators may also be provided with a valve to aid breathing.
The gasket itself is therefore a key factor in achieving reproducible, reliable fit of the respirator. Given the variation in facial features of wearers the gasket needs to be flexible enough and sized accordingly to fit around many different contours. One problematic area is around the nose of the wearer, where the respirator needs to fit closely and firmly against the skin to ensure minimal movement of the respirator during use as well as an airtight fit. To aid with fit, respirators are typically provided with a nose clip, such as a strip of metal, provided on the outer surface of the respirator and designed to be bent around the nose of the wearer to hold the respirator in place. One alternative to providing a nose-clip is to use a foamed in place gasket that fills the gap around the edge of the nose of the wearer, thus providing an improved fit. Such a solution is discussed in EP 1 614 361, where a rubber-like edge bead is moulded around the edge of the respirator, with deformable flanges included in the nasal region.
However, various issues may still arise with the use of a nose clip or other gasket: firstly, the inclusion of a nose clip may create additional manufacturing costs; secondly, the nose clip may be uncomfortable for some wearers since facial features and sizes vary greatly across the population of wearers; and thirdly, the fit achieved when not using a nose clip may be poorer in general without such close contact between the gasket and the skin of the wearer. Further, where fit is less than ideal, additional problems are encountered by wearers who also require eyewear to perform tasks, such as safety eyewear or prescription eyewear. For example, it may be difficult to wear safety glasses in the correct or a comfortable position if the base of the lenses or the frame impinges on the upper edge of the respirator or gasket. Even if worn in the correct position, a poorly fitting gasket encourages moist breath to escape the respirator and travel under the frame or lens of the eyewear, causing the eyewear to fog.